Acoustic echo cancellation and line echo cancellation both address similar problems, and are often based on the same technology. However, a line echo canceller generally cannot replace an acoustic echo canceller, because acoustic echo cancellation is a more difficult problem. With line echo cancellation there are generally only one or two reflections from telephone hybrids or impedance mismatches in the telephone line. These echoes are usually delayed by less than 32 ms, and do not change very frequently, if at all. With acoustic echo cancellation, the echo path is very complex (dozens or hundreds of reflections), lasts 100-200 ms, and can vary continuously during a conversation as people move around the room. Acoustic echo cancellers are therefore much more complicated devices. While line echo cancellers may have smaller price tags, they can’t perform under the conditions that acoustic echo cancellers can handle.